JP6434023B2 - Thermoelectric generator module and thermoelectric generator unit - Google Patents

Description

REFERENCE TO RELATED APPLICATION AND CLAIM OF PRIORITY This application is a non-provisional application of US Provisional Application No. 61 / 912,151, co-pending US Patent Application No. 61 / 912,151, filed December 5, 2013 And claims priority to the provisional application. By referring to the above-mentioned patent application, the entire disclosure is incorporated in the present application.

Government Benefit Statement This invention was made with government support under grant number DE-EE0004840 awarded by the US Department of Energy. Accordingly, the US government has certain rights in this invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to thermoelectric generators (TEG), and more particularly to a thermoelectric generator for use in an automobile.

  Automotive fuel efficiency can be improved by incorporating a thermoelectric generator (TEG) into the exhaust gas system. The thermoelectric generator converts exhaust heat from the internal combustion engine into electricity using the Seebeck effect. A typical thermoelectric generator includes a high temperature side heat exchanger, a low temperature side heat exchanger, a thermoelectric material, and a compression assembly. These heat exchangers are generally configured as metal plates with high thermal conductivity. Due to the temperature difference between the two surfaces of the thermoelectric module, electricity is generated using the Seebeck effect. When the high-temperature exhaust gas from the engine passes through the thermoelectric power generator, semiconductor charge carriers provided in the power generator diffuse from the high-temperature side heat exchanger to the low-temperature side heat exchanger. The formation of charge carriers generates an effective charge that generates an electrostatic potential Va (FIG. 2), while current is carried by heat transfer. If the exhaust gas temperature is 700 ° C. (about 1300 ° F.) or higher, the temperature difference between the high temperature side exhaust gas and the low temperature side refrigerant is several hundred degrees. In some automotive thermoelectric generators, this temperature difference can generate 500-750 W of electricity.

  The purpose of providing a compression assembly is to reduce the thermal contact resistance between the thermoelectric module and the heat exchanger surface. In the case of a thermoelectric generator for an automobile based on a refrigerant, the low-temperature side heat exchanger uses an engine refrigerant as a cooling fluid, whereas in the case of a thermoelectric generator based on an exhaust gas, the low-temperature side heat exchanger Uses ambient air as the cooling fluid.

For example, the vehicle exhaust gas system 10 shown schematically schematically in FIG. 1 includes an exhaust pipe 12, which, as an example, uses heated exhaust gas from an internal combustion engine 14 as a tail. To the exhaust system outlet 16 configured as a pipe. The exhaust gas system 10 may include additional exhaust gas components, such as mufflers, resonators, catalysts, etc., disposed between the internal combustion engine 14 and the outlet 16. In such an exhaust gas system, a thermoelectric power generation device 20 is incorporated, and more specifically, incorporated in the exhaust pipe 12, and heat generated by the exhaust gas is converted into electric energy / electric power by the thermoelectric power generation device 20. Converted. The thermoelectric generator 20 can store the electric energy generated in this way in a storage device S such as a rechargeable battery, and / or the thermoelectric generator 20 needs electric energy. In response, it can be supplied to various vehicle systems VS ₁ to VS _n . Examples of the vehicle systems VS _{1 to} VS _n include an engine control device, an exhaust gas system control device, a door lock system, a window opening / closing mechanism, and indoor lighting. Furthermore, a controller 22 may be provided to control the storage and use of electrical energy generated by the thermoelectric generator 20.

  For example, the thermoelectric unit 20 is composed of at least one material of a semiconductor and a semi-metal material having specific upper and lower temperature limits for efficient operation. If materials are exposed to an excessively high exhaust gas temperature exceeding the upper limit temperature, these materials may be damaged, and if the exhaust gas temperature is lower than the lower limit, generation of electric power is not possible. It can be efficient. Therefore, in the conventional system, it is necessary to provide the temperature control device 30 in the exhaust pipe 12 upstream of the thermoelectric generator 20. The temperature control device 30 can be in the form of a cooling device 30a, which cools the exhaust gas between the upper and lower temperature limits of the material used in the structure of the thermoelectric generator 20. Cool to a temperature within a specific temperature range. Next, the exhaust gas thus cooled is supplied to the inlet 32 of the thermoelectric unit 20. The exhaust gas passes through the thermoelectric generator 20, and the exhaust heat from the exhaust gas is converted into electric energy, and then the exhaust gas is discharged from the outlet 34 of the thermoelectric generator 20. This configuration consists of a non-bypass configuration, and according to this, all exhaust gas flows through the thermoelectric unit 20 and passes therethrough.

  The cooling device 30a can include many different types of cooling components. For example, the cooling device 30a can be a fluid-cooled heat exchanger, or the cooling device 30a can include an air injection device or a water injection device for cooling. Optionally, the cooling device 30a can also have a void pipe or forced air cooling device connected to the air injection device, which can provide cooling and potential reduction in thermal inertia, resulting in extremely rapid heating. Avoided. Further, the cooling device 30a may be configured to incorporate the function of the compression assembly described above, specifically, this directs the refrigerant or cooling action to the low temperature side heat exchanger of the thermoelectric generator 20. Is done by.

A key component of a thermoelectric generator is a thermoelectric (TE) module, which converts heat flux into electrical power. FIG. 2 depicts the general configuration and operation of a typical thermoelectric module 50. The thermoelectric module 50 is provided with n-type and p-type semiconductor legs 52 and 54 arranged alternately, and these semiconductor legs are electrically connected in series at a connection part 56. . The leg portion and the electrical connection portion can be sandwiched between the low temperature side substrate 60 and the high temperature side substrate 61 inside the thermoelectric unit 20. Due to the temperature gradient, a current 58 flows through each leg according to the Seebeck effect E _emf = −S ▽ T. Where S is the Seebeck coefficient which is a local material attribute, and ▽ T is the temperature gradient across the semiconductor leg.

The efficiency of heat to electricity conversion is the dimensionless figure of merit ZT:
ZT = σS ² T / (κ _el + κ _lat )
Is a material attribute represented by Where σ is the conductivity, S is the Seebeck coefficient, T is the temperature, κ _el is the electronic thermal conductivity, and κ _lat is the lattice thermal conductivity.

SUMMARY The present invention relates to a thermoelectric power generation (TEG) unit configured to be incorporated into a vehicle exhaust gas system. The unit includes a plurality of thermoelectric generator modules, each module having a plurality of electrically interconnected p-type and n-type thermoelectric material legs, each leg being The module extends between the high temperature side substrate and the low temperature side substrate of the module. In this case, the thermoelectric material for the legs is a half-Heusler compound having a thermoelectric figure of merit (ZT) greater than 1.0. According to one aspect, the thermoelectric material for the legs can have a doping level lower than 0.005 electrons or holes per unit cell.

  According to one characteristic, the thermoelectric material for the p-type legs is selected from the group of half-Heusler compounds comprising YNiSb, YNiBi, LaNiSb and LaNiBi. According to yet another feature, the thermoelectric material for the n-type legs is selected from the group of half-Heusler compounds comprising NbFeSb, VCoSn and TaFeSb. The doping of p-type and n-type compounds can be optimized by replacing some of the components of the compounds with certain elements or alloys.

Schematic which shows the vehicle exhaust gas system in which the thermoelectric power generator (TEG) was integrated. The figure which shows the thermoelectric unit (TE) of a thermoelectric power generator as shown in FIG. FIG. 7 is a graph showing an optimum doping level per unit cell when T = 400 ° C. in units consisting of holes and electrons for 28 half-Heusler (HH) compounds in a p-type region and an n-type region; The graph which made the error bar graph correspond to the range of the ZT value within 5% of the maximum value ZT. FIG. 4 is a graph showing electron relaxation time τ at energy μ ± κ _B T when T = 400 ° C. for optimally doped p-type and n-type half-Heusler compounds from FIG. 3. FIG. 4 is a graph showing the figure of merit ZT at T = 400 ° C. for the optimally doped p-type and n-type half-Heusler compounds from FIG. The phase diagram which shows the calculated phase of ternary system V-Co-Sn, Ta-Fe-Sb, Nb-Fe-Bi which represented the stable compound with the black circle and the unstable compound with the white circle.

DETAILED DESCRIPTION For the purposes of facilitating understanding of the principles of the invention, reference will now be made in detail to the embodiments illustrated in the drawings. However, it is needless to say that the following description is not intended to limit the scope of the present invention. Further, any alternatives or modifications to the illustrated embodiments are intended to be included in the present invention, and further to the principles of the present invention that would generally be assumed by one of ordinary skill in the art to which this disclosure relates. Of course, other applications are also included.

  Conventional thermoelectric materials such as BiTe (bismuth-tellurium) have low operating temperatures, and therefore there are limitations to using these thermoelectric materials in automotive applications and / or cool the exhaust gas stream. A device to do is needed. In recent years, several types of thermoelectric materials that exhibit high performance over a wide temperature range have been developed. Of those materials, some half-Heusler (HH) compounds are primarily n-type materials, including two groups of transition metals and three groups of metals and metalloids. However, the ZT value of the half-Heusler compound is doubtful, and the composition space of the half-Heusler compound has not yet been sufficiently investigated. Quantum mechanics simulation can be used to calculate ZT values for a number of different half-Heusler compounds and to identify new half-Heusler compounds that may be used in thermoelectric generators.

  In various material databases, 88 ternary compounds have so far been reported to have a half-Heusler structure, which is summarized in the overview of the reference [1] shown in the appendix. The target half-Heusler compound is selected based on the following two criteria. That is, 1) a material composed of inexpensive elements abundant on the earth, and 2) a semiconductor material. The latter condition is satisfied by selecting from compounds having 18 valence electrons per chemical unit, as described in reference [2] in the appendix. By applying the second condition, the list is narrowed from 88 half-Heusler compounds to 15 half-Heusler compounds. Furthermore, 13 hypothetical compounds have been identified by replacing the chemical elements of these 15 existing half-Heusler compounds with other elements that belong to the same group and have similar covalent radii. Table 1 below shows a compound list consisting of 28 half-Heusler compounds (15 existing compounds and 13 hypothetical compounds indicated by (?)).

  The electron transport coefficients for these 28 half-Heusler compounds listed in Table 1 should be calculated by solving the Boltzmann Transport Equation (BTE) for the electrons by single mode relaxation time approximation (SMTRA) using the BoltzTraP program. Can do. For this, see reference [3]. For these calculations, the electronic band structure and the electron relaxation time τ, which is the central quantity of the BTE theory, are required as inputs. The electronic band structure is generally calculated using density functional theory (DFT), while τ is assumed to be constant (independent of electron energy, chemical potential μ and temperature T). Although the DFT method is fast and robust, it is known to estimate the electronic band gap of a semiconductor smaller than the actual one. Therefore, a more accurate (but more computationally expensive) band structure calculation method can be used, which is known as the GW method. Using the DFT and GW calculations performed on six half-Heusler compounds selected from Table 1 using the packages of Quantum ESPRESSO (see reference [4]) and BerkeleyGW (see reference [5]) The band gap (unit: eV) shown in Table 2 below was calculated.

  The similarity between the DFT and GW values in Table 2 suggests that DFT can accurately predict the band structure for half-Heusler compounds, as opposed to most semiconductors. is there. Therefore, the DFT method was used for the band structure calculations of the remaining 22 half-Heusler compounds listed in Table 1.

At high temperatures typical of thermoelectric generator operation, it is electron-phonon scattering that primarily contributes to τ. First-principles formulas for electron-phonon interactions can be applied as outlined in reference [6] listed in the appendix, followed by EPA (electron-phonon averaging). An approximation is made. According to the reference [6], the inverse element τ is expressed as an element of an electron-phonon interaction matrix, the number of electrons and phonons occupied, and an electron density state. According to the EPA approximation, the elements of the electron-phonon interaction matrix are calculated in density functional perturbation theory (DFPT) using the Quantum ESPRESSO package (Ref. [4]) and averaged for electron and phonon momentum. And then the averaged quantities are used to calculate the inverse τ according to the equation in reference [6]. The calculated τ is substituted into the BTE of the electron, and then the BTE is solved to calculate the conductivity σ, the thermal conductivity κ _el and the Seebeck coefficient S. The remaining amount substituted into the ZT equation, ie, the lattice thermal conductivity κ _lat , can be calculated by solving the phonon BTE. However, previous efforts to optimize thermoelectric materials have revealed that κ _lat of half-Heusler compounds can be greatly reduced from their crystalline values by alloying (mass disorder) and nanostructuring. ,That's what it means. Refer to documents [7] and [8] for this. Therefore, the value of κ _lat is set to 2.2 W (mK), which is the value of two optimized compounds when measured at T = 400 ° C., namely n-type Hf _0.75 Zr _{0. .25} NiSn _0.99 Sb _0.01 and p-type Hf _0.8 Ti _0.2 CoSb _0.8 Sn _0.2 average for κ _lat values. Refer to documents [7] and [8] for this.

  The electron transport coefficients and ZT values of the 28 half-Heusler compounds listed in Table 1 can be calculated as a function of the chemical potential μ at an average operating temperature T = 400 ° C. For each half-Heusler compound, the ZT vs. μ curve has two maximum values when μ approaches the valence band top (VBM) and the conduction band bottom (CBM). These two values of μ correspond to optimum doping levels in the p-type region and the n-type region, respectively. The resulting doping level is shown in the graph of FIG. These doping levels are not the same as the dopant concentration of these compounds due to inherent defects that cause self-doping. For example, the unique ZrCoSb and TiZNiSn compound is an n-type material having a self-doping level of about 0.1 electrons per unit cell. For this, see references [9] and [10]. Nevertheless, the following correlation exists between the doping level and the dopant concentration. That is, as shown in FIG. 3, the optimum doping level for n-type (Ti, Zr, Hf) NiSn is about 0.005 electrons per unit cell, and p-type (Ti, Zr, For Hf) CoSb, there are about 0.055 holes per unit cell, while the optimum dopant concentrations for these materials are x = 0.01 and x = 0.2, respectively (reference [7] , [8]).

For illustrative purposes, FIG. 4 shows electrons in an optimally doped p-type and n-type half-Heusler compound at an energy μ ± k _B T (where k _B is Boltzmann's constant) at T = 400 ° C. The value of τ is shown. As shown in FIG. 4, τ varies by more than two orders of magnitude for different half-Heusler compounds or depending on whether the same half-Heusler compound is doped p-type or n-type. ing. This suggests that the approximation with τ constant as widely adopted in the literature is inappropriate for half-Heusler compounds (and generally semiconductor materials).

  FIG. 5 shows the figure of merit ZT for T = 400 ° C. for optimally doped p-type and n-type half-Heusler compounds. The data analysis shown in FIG. 5 reveals that the (Ti, Zr, Hf) NiSn compound has one of the largest ZT values among the n-type half-Heusler compound materials. It is. This result is consistent with the experimentally optimized n-type (Ti, Zr, Hf) NiSn compound. For this, see reference [7]. However, according to the calculation, four n-type compounds (one existing compound and three hypothetical compounds) having a ZT value larger than that of the (Ti, Zr, Hf) NiSn compound are confirmed. These compounds include NbFeSb, which is an existing compound, and VCoSn, TaFeSb, and NbFeBi, which are theoretical compounds. According to the calculation, the p-type (Ti, Zr, Hf) CoSb compound has a moderate ZT value as compared with the n-type (Ti, Zr, Hf) NiSn compound. This measurement is also consistent with experimental data. For this, see reference [8]. According to the calculation, four p-type compounds (all existing) having a ZT value larger than that of the (Ti, Zr, Hf) CoSb compound are confirmed, that is, these compounds include YNiSb, LaNiBi, LaNiSb and YNiBi.

  Three hypothetical half-Heusler compounds can be recognized as promising n-type materials: VCoSn, TaFeSb, NbFeBi. To check the stability of these hypothetical compounds, as well as the energies of all known compounds of the ternary V—Co—Sn, Ta—Fe—Sb and Nb—Fe—Bi, The energy of can be calculated. Convex hulls are constructed in the ternary space of each hypothetical compound. The resulting ternary phase diagram is shown in FIG. 6, which shows that stable and unstable compounds (inside and outside the convex hull) are black circles (stable) and white circles. It is indicated by (unstable). The hypothetical compound of interest is represented by a circle at the center of the triangle. As shown in FIG. 6, VCoSn and TaFeSb are stable, whereas NbFeBi is unstable. According to the analysis of the convex hull, it is predicted that the production energies of VCoSn and TaFeSb are 1 mev / atom and 68 meV / atom, respectively, while the production energy of NbFeBi is -197 meV / atom. Fortunately, unstable NbFeBi has the lowest ZT value of the three hypothetical compounds shown in FIG.

The maximum ZT values and optimum doping levels for the seven half-Heusler compounds proposed here (four p-type compounds and three n-type compounds) are shown in Table 3 below. In order to achieve the ZT values listed in Table 3, these compounds are doped to an optimal level and their lattice thermal conductivity is reduced to κ _lat = 2.2 W / by alloying (mass disorder) and nanostructuring. Reduce to (mK). For the compounds listed in the left half of Table 3, the p-type doping is replaced by replacing the Y or La part with Mg, Ca, Sr or Ba, the Ni part with Co, and the Sb or Bi part with C. , Si, Ge, Sn or Pb can be achieved. For the compounds listed in the right half of Table 3, n-type doping replaces the Fe portion with Mn by replacing the V, Nb or Ta portion with Ti, Zr or Hf, and the Co portion with Fe. This can be achieved by replacing the Sn portion with B, Al, Ga or In and replacing the Sb portion with C, Si, Ge, Sn or Pb. For the compounds listed in Table 3, the mass disorder can be determined by alloying Y, La and lanthanides, by alloying V, Nb and Ta, by alloying Sn, C, Si, Ge and Pb, and Sb, This can be achieved by alloying Bi, N, P and As.

Table 3
p-type n-type compound ZT doping compound ZT doping
YNiSb 1.61 0.003 NbFeSb 1.40 0.001
LaNiBi 1.44 0.003 VCoSn 1.34 0.003
LaNiSb 1.26 0.004 TaFeSb 1.31 0.001
YNiBi 1.22 0.003

  According to one aspect of the present invention, the p-type and n-type half-Heusler compounds listed in Table 3 are used in the semiconductor legs 52 of the thermoelectric module 50 (FIG. 2) incorporated in the thermoelectric generator unit 20 (FIG. 1). , 54 as a thermoelectric material. The half-Heusler compound is selected depending on stability, high ZT and lattice thermal conductivity of about 2.2 W / (mK) or less.

  Doping p-type compounds by replacing the yttrium or lanthanum component part with an alkaline earth metal, replacing the nickel part with cobalt, and / or replacing the antimony or bismuth part with a non-metal or base metal. Can be optimized.

  Also, doping of the n-type compound can be accomplished by replacing the 5B transition metal with a 4B transition metal, replacing the iron portion with manganese, or replacing the cobalt portion with iron, and / or tin 3A. It can be optimized by substituting with a series element or by substituting antimony with a 4A series element.

According to another aspect, the mass disorder of the compounds listed in Table 3 can be achieved by alloying yttrium and lanthanide, alloying 5B transition metal, alloying 4A series elements, and alloying 5A series elements. Can be achieved.
The thermoelectric material for the p-type legs may be a half-Heusler compound consisting of an alloy of yttrium, lanthanide or alloys thereof and nickel and antimony, bismuth or alloys thereof. The thermoelectric material for the n-type legs can be a half-Heusler compound consisting of an alloy of niobium, vanadium, tantalum or alloys thereof, iron or cobalt, and antimony or tin.

  The present disclosure is to be regarded as illustrative and not restrictive in character. Moreover, while only some embodiments have been presented, it is understood that any changes, modifications and further applications made within the scope of the present disclosure are desired to be protected.

Appendix The following references are cited in this specification. These disclosures are incorporated herein by reference.
[1] Winnie Wong-Ng and J. Yang "International Center for Diffraction Data and American Society for Metals database survey of thermoelectric half-Heusler material systems." Powder Diffraction Vol. 28, No. 1, p. 32, 2013.
[2] BRK Nanda and I. Dasgupta "Electronic structure and magnetism in half-Heusler compounds." Journal of Physics: Condensed Matter Vol. 15, No. 43, p. 7307, 2003.
[3] Georg KH Madsen and David J. Singh "BoltzTraP. A code for calculating band-structure dependent quantities." Computer Physics Communications, Vol. 175, No. 1, p. 67, 2006.
[4] P. Giannozzi, S. Baroni, N. Bonini, M. Calandra, R. Car, C. Cavazzoni, D. Ceresoli, GL Chiarotti, M. Cococcioni, I. Dabo, A. Dal Corso, S. de Gironcoli, S. Fabris, G. Fratesi, R.
Gebauer, U. Gerstmann, C. Gougoussis, A. Kokalj, M. Lazzeri, L. Martin-Samos, N. Marzari, F. Mauri, R. Mazzarello, S. Paolini, A. Pasquarello, L. Paulatto, C. By Sbraccia, S. Scandolo, G. Sclauzero, AP Seitsonen, A. Smogunov, P. Umari and RM Wentzcovitch "QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials." Journal of Physics: Condensed Matter Vol. 21, No. 39, page 395502, 2009 edition.
[5] "BerkeleyGW: A Massively Parallel Computer Package for the Calculation of the Quasiparticle and Optical Properties of Materials and Nanostructures." Computer Physics Communication by J. Deslippe, G. Samsonidze, DA Strubbe, M. Jain, ML Cohen and SG Louie Vol.183, No.6, p.1269, 2012.
[6] G. Grimvall "The Electron-Phonon Interaction in Normal Metals." Physica Scripta Vol. 14, No. 1-2, p. 63, 1976.
[7] "Enhancement in Thermoelectric Figure-Of-Merit of an N-Type Half-Heusler Compound by the Nanocomposite Approach." Advanced Energy Materials 1st by Giri Joshi, Xiao Yan, Hengzhi Wang, Weishu Liu, Gang Chen and Zhifeng Ren Volume 4, page 643, 2011 edition.
[8] "Stronger phonon scattering by larger differences in atomic mass and size in p-type half" by Xiao Yan, Weishu Liu, Hui Wang, Shuo Chen, Junichiro Shiomi, Keivan Esfarjani, Hengzhi Wang, Dezhi Wang, Gang Chen and Zhifeng Ren -Heuslers Hf _1-x Ti _x CoSb _0.8 Sn _0.2 . "Energy & Environmental Science Vol. 5, No. 6, p.
[9] Y. Xia, S. Bhattacharya, V. Ponnambalam, AL Pope, SJ Poon, and TM Tritt, "Thermoelectric properties of semimetallic (Zr, Hf) CoSb half-Heusler phases." Journal of Applied Physics Vol. 88 No. 4, page 1952, published in 2000.
[10] "Electronic transport properties of electron- and hole-doped semiconducting C _1b ," by Siham Ouardi, Gerhard H. Fecher, Benjamin Balke, Xenia Kozina, Gregory Stryganyuk, Claudia Felser, Stephan Lowitzer, Diemo Kodderitzsch, Hubert Ebert and Eiji Ikenaga. Heusler compounds: NiTi _1-x MxSn (M = Sc, V). “Physical Review B, Vol. 82, No. 8, No. 085108, 2010.

Claims (10)

A thermoelectric generator module having a plurality of electrically interconnected p-type and n-type thermoelectric material legs, each leg between a high temperature side substrate and a low temperature side substrate of the module Extended,
The thermoelectric material for the legs is a half-Heusler compound having a thermoelectric figure of merit (ZT) greater than 1.0;
The thermoelectric material for the p-type legs is selected from the group of half-Heusler compounds including LaNiSb and LaNiBi, or
The thermoelectric material for the n-type legs is selected from the group of half-Heusler compounds comprising VCoSn and TaFeSb.
Thermoelectric generator module. The thermoelectric material for the legs has a doping level lower than 0.005 electrons or holes per unit cell,
The thermoelectric generator module according to claim 1. Doping of the half-Heusler compound for the p-type legs, by replacing part of the components La lanthanum and alkaline earth metals, or by replacing part of the nickel and cobalt, or, antimony or bismuth Optimized by replacing the part with non-metal, semi-metal or base metal,
The thermoelectric generator module according to claim 1. The alkaline earth metal is selected from magnesium, calcium, strontium and barium;
The thermoelectric generator module according to claim 3. The non-metal or the base metal is selected from carbon, silicon, germanium, tin and lead;
The thermoelectric generator module according to claim 3. The doping of the half-Heusler compound for the n-type leg replaces the 5B transition metal with a 4B transition metal, or replaces the iron part with manganese, or replaces the cobalt part with iron. Or by replacing tin with a 3A series element or by replacing antimony with a 4A series element.
The thermoelectric generator module according to claim 1. The 4B transition metal includes titanium, zirconium and hafnium.
The thermoelectric generator module according to claim 6. The 3A series elements include boron, aluminum, gallium and indium.
The thermoelectric generator module according to claim 6. The elements of the 4A series include carbon, silicon, germanium, tin and lead.
The thermoelectric generator module according to claim 6. A thermoelectric power generation (TEG) unit configured to be incorporated into an exhaust gas system of a vehicle,
The thermoelectric generator unit includes a plurality of thermoelectric generator modules according to claim 1,
Thermoelectric generator unit.

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